The present invention relates to a catheter or a microcatheter for macerating a thrombus and to a method for thrombus maceration with a catheter or a micro catheter.
In an acute stroke, a blockage is formed within an artery by a thrombus or clot. One goal in treating stroke is removal of the blockage caused by the thrombus or clot as soon as possible. It is widely believed that if the blockage can be removed within the first six hours after the stroke, the chances for patient recovery with little or no neurological deficit is significantly increased. Many practitioners believe the window of opportunity is limited to the first three hours. One method of thrombus removal has included a step of dislodging the thrombus from walls of a vascular system and then removing the thrombus from the vascular system with a suction device. The Willard et al., U.S. Pat. No. 5,419,774, issuing May 30, 1995, describes a method and a device for removing a thrombus from a vascular system using this general approach. The device is used in a saphenous vein graft and is introduced without a guide wire in order to avoid a possible dislodgment of the thrombus prematurely. With this device, thrombus material is pulled into a chamber at a distal end of a catheter. The rate of pulling is regulated by pressure exerted on an irrigation solution as well as a level of vacuum pressure applied to a discharge lumen and the timing and speed of a cutter stroke.
The thrombus may also be dissolved because the thrombus is comprised of components that can be dissolved or "lysed" with drugs such as urokinase and strepto-kinase. In conventional stroke therapy these "lytic" drugs are administered via a systemic intravenous (I.V.) administration. The drugs are infused throughout the entire circulatory system so that only a very diluted concentration of drug actually contacts the thrombus.
A more aggressive treatment is to deliver the lytic drugs directly to the thrombus with a catheter. The catheter is typically positioned adjacent to the thrombus and the drugs are infused directly into the thrombus. With this form of administration, the drugs, in much higher concentrations, reach the thrombus for an improved effectiveness. However, these higher concentrations may be inadequate to dissolve a single, relatively large thrombus mass.
The Kotula et al., U.S. Pat. No. 5,569,275, issuing Oct. 29, 1996, describes a thrombus macerating device that includes an elongate, flexible shaft which can be guided along a vascular path. A rotor or impeller with blades is affixed to the shaft adjacent to its distal end. A drive mechanism is provided for rotating the shaft and the rotor which is attached to the shaft. The rotor is retained within a rotor housing and rotates within the housing. The rotor housing includes a cylindrical wall that surrounds the rotor and that has at least three ports spaced angularly about the circumference of the housing. As the rotor is rotated, it will tend to draw blood into the housing in a proximal direction and expel the blood out through the ports. The blood then tends to be drawn back into the distal end of the housing and through the rotor again. This movement sets up a recirculating vortex which repeatedly passes the blood across the blades.
When the blood is ejected through the ports in the housing within a vascular channel, the blood will act against the wall of the channel. This action maintains the housing in a position which is spaced away from the surrounding vascular wall. By spacing the ports angularly about the circumference of the housing, the force exerted by the ejected blood tends to maintain the housing and rotor carried within the housing in a position that is centered within a vascular channel.
The Kotula et al., U.S. Pat. No. 5,284,486, issuing Feb. 8, 1994, describes a mechanism for breaking down a thrombus with rotating blades. The thrombus is broken down into particles which are fine enough to be left in the vascular system without a significant risk of forming additional thrombi. The mechanism also includes another mechanism to ensure that rotating blades of the mechanism do not directly contact walls of a vessel, but remain centered within the vessel. The mechanism includes an elongate, flexible shaft with a rotor or impeller having blades affixed to the shaft adjacent its distal end. A drive mechanism is provided for rapidly rotating the shaft and the rotor attached to the shaft. The rotor is retained within a rotor housing and rotates within the housing. The rotor housing includes a generally cylindrical wall that is substantially surrounding the rotor and that has at least three ports spaced angularly about the circumference of the housing. As the rotor is rotated, it will tend to draw blood into the housing in a proximal direction and expel the blood out through the ports. The blood then tends to be drawn back into the distal end of the housing and through the rotor again. This activity sets up a recirculating vortex which repeatedly passes the blood across the blades.